This invention relates to the preparation of epoxy resins. In one aspect, the invention relates to a catalyzed process for reacting a hydroxyl group-containing compound with an epoxy-containing compound. In a further aspect, the invention relates to a catalyst for use in an epoxy fusion process.
Epoxy compounds are well known and include many compounds of varying molecular weight and epoxy equivalent weight. To simplify the production of a large number of epoxy compounds that vary mainly in molecular weight, it is common practice to manufacture a single epoxy compound of relatively low molecular weight and react the epoxy compound with a compound containing phenolic hydroxyl groups in the presence of a catalyst so as to obtain phenolic hydroxy ether compounds of desired higher molecular weight. The conventional catalysts employed are inorganic bases or tertiary amines, which are also effective catalysts for competing reactions of epoxides with alcoholic hydroxyl groups, homopolymerization of epoxy groups and the like. As a result, the product obtained is a mixture of polymers and resins with varying degrees of molecular weight, chain branching and end group functionality. More recent catalysts with improved selectivity include phosphonium halides as disclosed in U.S. Pat. Nos. 3,477,990 and 4,438,254.
When many of these high-selectivity catalysts are mixed with the epoxy resins to produce a "pre-catalyzed" epoxy composition, the storage stability of the composition at elevated temperatures is not acceptable for many applications because of the reduced activity of the stored resin. U.S. Pat. No. 4,320,222 discloses the use of a precatalyzed polyepoxide containing a phosphonium halide catalyst and an alkali metal halide or hydroxide stabilizer additive as one approach to this problem.
An alternate approach is to control the reaction process steps under strict conditions so as not to deactivate the catalyst. For example, U.S. Pat. No. 4,438,254 describes the use of phosphonium salt catalysts which are water-sensitive and recommends careful control of water and temperature in the reaction mixture.
Given the storage instability of precatalyzed epoxy resin systems, it would be desirable to develop precatalyzed epoxy resin systems which have good storage stability at high temperatures and high activity in the presence of water.